Flash Photography with Canon EOS Cameras - Part I.
Copyright © 2001-2002 NK Guy
Version 1.2. February 22, 2002.
Please note that this page now has a new URL; noted below.
http://photonotes.org/articles/eos-flash/
Flash photography has always been a very difficult technique to master on any camera system. It’s easy to take a snapshot of your friends in a restaurant and get that hideously blown-out rabbit-in-the-headlights look from built-in automatic flash. But using electronic flash well - achieving natural-looking images - is quite tricky.
This is largely, of course, because the human eye can’t fully discern the effects of a flash burst at the time an image is taken - the brief pulse of light is just too short for us to process. And you can’t even see the flash if you’re looking through the viewfinder of an SLR camera anyway, as the mirror will have been raised for the duration of the flash.
So you have to read manuals and experiment. But with film-based photography there’s a long lag time in the feedback loop - you have to take your film in to be processed before you see what worked and what didn’t. Taking notes can be cumbersome because of the highly automated nature of modern flash. Even professionals don’t rely entirely on their experience and flash meters and do test shots with a Polaroid instant film back in studio flash situations. Digital photography has one of the benefits of shortening this feedback loop considerably, but that doesn’t really help those of us who still use film.
So, here’s some information that may help you understand some of the mysteries of flash photography with Canon EOS camera equipment. Much of the information presented herein is fairly general in nature and thus covers similar flash systems used by other manufacturers, but much is very specific to Canon EOS products.
Note that this document covers Canon EOS products, including digital EOS cameras. Canon’s PowerShot series of digital cameras can use Speedlite EX-series flash units, but since they aren’t EOS cameras there are significant differences in the way they work.
Table of Contents
Part I - Flash Photography with Canon EOS Cameras.
Top Ten Frequently Asked EOS Flash Questions.
1 - My camera already has a built-in flash. Do I need an external one? If so, what kind?
2 - I’m not happy with my flash photos. The lighting always looks harsh and unflattering.
3 - Are my friends possessed by demonic powers? Their eyes are glowing an evil red!
4 - I took a flash photo and there’s a curved shadow at the bottom of the photo.
5 - I took two flash photos in rapid succession and the second one is totally dark.
6 - I’ve put a diffuser or reflector on my flash. Do I have to compensate for this somehow?
7 - I tried to take a flash photo and the camera wanted a really slow shutter speed.
8 - I tried taking a flash photo and the camera wouldn’t let me set a very high shutter speed.
9 - I took a flash photo and the background is pitch black or very dark.
10 - My camera meters in P and Av modes very differently when I have a flash turned on.
Flash metering systems used by Canon EOS.
Controlling flash exposure.
Flash metering principles.
TTL (through the lens) flash metering.
Refinements to TTL flash, including Canon AIM.
A-TTL (advanced TTL).
Limitations of A-TTL.
E-TTL (evaluative TTL).
Limitations of E-TTL.
FP (focal plane) flash mode.
TTL and E-TTL and EOS film cameras.
TTL and E-TTL and EOS digital cameras.
Type A and type B bodies.EOS system compatible flash units.
Internal flash.
Basic (PIC) modes and external flash units.
Canon external flash unit types.
Nomenclature of external flash units.
Older Canon Speedlite flash units.
Hotshoe flashes.
Handle-mount (grip) flash.
Macro flash.
Third-party flash units.
Achiever.
Metz.
Sigma.
Soligor.
Sunpak.
Vivitar.
Other flashes.Part II - EOS flash photography modes.
Subject and Background in flash photography.
Fill flash.
Fill flash ratios.
Auto fill reduction.
Slow shutter sync.
X-sync (flash sync) speed.
Maximum X-sync speed and EOS bodies.EOS flash photography confusion.
Program (P) mode flash.
Tv (shutter priority) mode flash.
Av (aperture priority) mode flash.
Manual (M) exposure mode flash.
Multiple flash units.
Metering patterns for the background when using flash.
Flash metering patterns.
Do not focus and recompose.Strobe and flash.
Inverse square law.
Guide number.
Exposure values (EV).
Dedicated or non-dedicated flash units.
Shoe mount.
The redeye effect.
Redeye reduction.
The first curtain sync problem.
Second-curtain sync.
Colour temperature theory.
Colour temperature and film.
Colour temperature and flash photography.
Colour filters.
Limitations of filters.
Mireds.
Wratten numbers.
Trigger circuit voltage.
Slave flashes.
Flash meters.
Flash sync trivia.Part III - Common EOS flash features.
Bounce flash - swivel and tilt.
Zooming flash heads.
Flash head coverage.
AF assist light.
Camera-specific notes on AF assist lights.
Flash exposure compensation (FEC).
Which bodies/flash units have FEC.
List of which bodies/flash units have FEC.
Flash exposure lock (FEL).
Flash exposure bracketing (FEB).
Enabling second curtain sync.
List of which flash units and camera bodies have second-curtain sync.
Range warning.
Manual flash.
Flash exposure level.
Rapid-fire mode.
Stroboscopic flash.
Setting stroboscopic flash.
Flash exposure confirmation.
Wireless remote control.
Modelling flash.
Save Energy (SE) mode.
High-voltage connector.
PC terminals/sockets.
Custom functions.
Test flash (manual firing).
Manual flash triggering for light painting.
Noise.
Flash safety.Extension cords.
Flash diffusers.
Flash brackets.
External battery packs.
Flash extenders
Power source options for external flash units.
Standard AA non-alkaline (zinc carbon) cells.
Standard AA alkaline cells.
Rechargeable nickel-cadmium (NiCad) cells.
Lithium AA cells.
Rechargeable nickel metal hydride (NiMH) cells.
External battery pack.Quality of light.
General flash photography.
Shooting indoors in a small space.
Shooting outdoors or indoors in a large space.
Learning more about flash photography with EOS cameras is hard as there’s relatively limited information available on the topic. Canon’s manuals tend to be fairly short, and not much information has been published about the flash algorithms used by EOS cameras. There’s a brochure on the topic - Canon’s “Flash Work,” but unlike the excellent and similarly titled book “Lens Work,” the flash brochure does not go into much detail. Hove/Silver Pixel Press published a book on the Canon Speedlite 540EZ flash unit, which also briefly described other Canon flash units sold at the time, but the book is now apparently out of print.
Canon USA did publish two technical booklets on the subject in the early 1990s - the “Canon Speedlite Reference Guide” and the smaller “Canon EOS Speedlite System.” However, these are now out of print and don’t cover E-TTL technology. The Speedlite Reference Guide is a very useful resource for learning more about TTL and A-TTL flash, however. Many thanks to Brett Cheng for mailing me a copy!
When the Elan II (EOS 50) was released, Canon USA’s Chuck Westfall provided some valuable information that Mark Overton wrote up in the form of an FAQ. This document is very useful, but somewhat terse - it doesn’t cover a lot of the terminology and background. It also deals primarily with one camera/flash combination - the Elan II and the Speedlite 380EX. So I decided to write a somewhat more detailed account of how EOS flash works.
The document you are currently reading is, however, extremely long and detailed. So if you want a quick précis of EOS flash technology you should probably consult the Westfall/Overton FAQ on Bob Atkins’ Web site.
Finally, please note that I have no particular insight into or access to the mysterious ways of Canon’s flash engineers. I wrote this document partly because I thought it might be helpful to others and partly because explaining something is a great way to learn something yourself. But there may, of course, be technical errors in this document. If you spot any errors or ambiguous or vague sections, Please send feedback!
Top Ten Frequently Asked EOS Flash Questions.
Before we start, however, I’d like to provide quick answers to the top ten Frequently Asked EOS Flash Questions, since they come up an awful lot.
1) My camera already has a built-in flash. Do I need an external one? If so, what kind?
This question crops up all the time on discussion forums, much to the irritation of oldtimers. And their irritation usually arises for two simple reasons. First, they’re grumpy cantankerous curmudgeons and second, the question is sort of meaningless without knowing what your photographic requirements and interests are.
It’s very much like asking, “What car should I buy?” The answer depends on your needs and budget. But here’s a brief overview of what you should consider.
If you just want something to take snapshots with, a built-in popup flash is probably sufficient. It can’t produce much light and so doesn’t have a lot of range, but then friends in restaurants aren’t going to be very far from you. It has a harsh quality, but for snapshots most people don’t seem to mind much. And internal flash units are convenient - you can’t lose them unless you lose the whole camera, and they don’t add any additional weight or bulk.
However, if you want to get into more advanced photography you’ll probably want either to buy a good external flash unit or else eschew flash as often as possible and rely more on available light. As noted above, the light from an internal flash unit is very harsh, whereas external units let you soften the light by bouncing it off of walls or ceilings, or attaching light-softening diffusers. Most importantly, an external flash unit can be taken off the camera - either with an extension cord or wireless. This is important since on-camera flash provides unnatural head-on lighting. How often outside of a cave do you see people in real life illuminated by a light source on your forehead?
At this point it’s largely a matter of how much you want to spend and how much weight you want to carry around. However, unlike cars, there’s a fairly basic range of options to choose from.
The top of the line 550EX flash can do anything a portable flash unit can be expected to do, but it’s very large and both costs more and weighs more than a brand new low-end EOS camera. Midrange units like the 420EX are smaller and lighter, but don’t have manual controls so you can only use them in fully automatic mode. Tiny units like the 220EX don’t provide much more light than a built-in flash, but they’re small and lightweight and can be moved off-camera with a cord. Finally, there are a number of third-party (non Canon) flash units you could consider.
If you have a type A camera you’re best off buying an EX-series (E-TTL capable) flash to take full advantages of the newer features. If you have a type B camera you’re probably best off buying a nice used EZ series (non E-TTL) flash unit, unless you’re planning on upgrading to a type A camera in the future and want to invest in accessories that are fully compatible. (putting an EX flash on a type B camera means you can’t use A-TTL, but I don’t think that’s much of a loss) If you don’t know whether your camera is a type A or type B model, consult this list. Finally, if you have a digital Canon camera such as a D60 or PowerShot then you don’t have a choice - you must get an EX-series flash unit.
Nonetheless, remember that flash is no panacea for photographic lighting problems. It’s obviously a valuable tool, but often the best way to ruin a nice picture is to blast tons of light onto the scene with a flash unit. Available light photography forces you to slow down and consider the light around you, which ultimately can help you become a better photographer.
2) I’m not happy with my flash photos. The lighting always looks harsh and unflattering.
Flash is like that. Basically, soft lighting is light which originates from a large area. Portable camera flashes, by contrast, have very small light-producing areas and, therefore, produce very hard-edged light with pronounced shadows.
The easiest way to soften the lighting in your flash photos is to bounce the light from the flash unit off a large white surface. Walls and ceilings work for this, as do portable folding reflectors. You can also buy diffusers that attach to your flash that help a little bit as well. For more information have a look at the section on quality of light.
3) Are my friends possessed by demonic powers? Their eyes are glowing an evil red!
Assuming you mean their eyes glow in your photos and not real life, this is the “redeye” effect; a common problem with the internal flash units built into cameras. It’s caused by the light from the flash unit reflecting off the red blood vessels lining the interior of the eye. The light shines back into the camera, resulting in the famous red glow.
The easiest way to minimize the risk of redeye is to use an external flash unit rather than a built-in flash. The problem is fully explained in the redeye section of this document, as is the related problem of greeneye in cats and dogs.
4) I took a flash photo and there’s a curved shadow at the bottom of the photo.
You’re using the camera’s internal flash and you also have a very large lens installed or a lens with a big lens hood. Either way, something is blocking the light from the internal flash.
To fix the problem you could try a different lens, zoom wider if the lens is extended (ie: shorten the lens if it’s a zoom lens), remove the lens hood or use an external flash unit. It’s also possible that you’re too close (a metre or less) to the subject.
5) I took two flash photos in rapid succession and the second one is totally dark.
All flash units take a few seconds to charge up between flash bursts. Some flash units have “rapid-fire” abilities which let them fire the flash even if the internal capacitor is fully charged - but others don’t.
So if your second photo is dark it probably means that your flash unit lacks rapid-fire capabilities. You have to wait for the unit to charge up fully (and the pilot light on the back of the unit goes on) before taking the second photo. However, if your flash does have rapid-fire capabilities then you probably took the second photo too quickly and the flash unit hadn’t enough time to recharge to an adequate power level.
Note that different types of batteries charge up the flash at different speeds, so if this is a consistent problem you should look into your battery options.
6) I’ve put a diffuser or reflector on my flash. Do I have to compensate for this somehow?
Diffusers of any kind obviously reduce the amount of light that your flash unit produces. You’ll find a similar effect if you bounce the light from your flash unit off a wall or into a photographic umbrella.
However, so long as you’re using automated (TTL, A-TTL or E-TTL) metering then the camera will compensate automatically. There is no need to adjust anything.
You’ll have decreased range, but you shouldn’t have any exposure problems unless you’re too far away from the subject and the decreased range now means you’re out of range. Diffusers can easily cost you at least half your flash range, depending on the type.
7) I tried to take a flash photo and the camera wanted a really slow shutter speed.
This occurred because you are trying to take a flash photo in low-light conditions and the camera is in Av (aperture priority) mode or the night PIC (icon) mode if your camera has it.
In Av, night and Tv (shutter speed priority) modes the camera meters for ambient (existing) light and fills in the foreground subject using the flash. It does not assume that the primary light source is the flash, and therefore the shutter speed it sets is the same as it would set if you weren’t using flash at all.
In low light this results in slow shutter photography. If the shutter speed is very long you will, therefore, need a tripod to avoid motion blur during the exposure.
Alternatively you can switch to full auto (green rectangle) or Program (P) mode, which automatically expose for the flash-illuminated subject and not the background. These modes try to ensure that the shutter speed is high enough to let you handhold the camera without a tripod. The drawback of P and basic modes is that photos taken in dimly lit areas usually end up with black or poorly lit backgrounds.
8) I tried taking a flash photo and the camera wouldn’t let me set a very high shutter speed.
Each camera model has a top shutter speed that can be used with flash. This is known as its flash sync or X-sync speed, and varies from 1/90 sec on low-end cameras to 1/250 on pro cameras. (1/500 sec on the digital 1D)
If you have a newer camera and an EX series flash you can use FP mode to circumvent this limit - see the FP section for more details.
9) I took a flash photo and the background is pitch black or very dark.
This is the flip side of question 7. In P (program) mode and all flash-using PIC (icon) modes except for night mode (if your camera has it) the camera uses the flash as the primary light source for the foreground subject.
If the ambient light levels are low, therefore, the background will turn out very dark. This is because the flash is not illuminating the background and the shutter speed is too short to expose adequately for background areas.
Remember that the light from any battery-powered flash is somewhat limited. You can’t expect a small flash unit to light up the Grand Canyon or Eiffel Tower. You can only reasonably expect it to light up people standing in the foreground or close backgrounds such as room interiors.
To avoid this problem of black backgrounds you will need to take a photo in Av, Tv or M modes, as mentioned in question 7. If the ambient lighting is very low you may need a tripod to avoid motion blur for the time required to expose the background adequately. Using fast film (eg: ISO 800) and wide lens apertures (the smaller the f stop you can get on your lens) will help bring up the background as well.
10) My camera meters in P and Av modes very differently when I have a flash turned on.
That’s how EOS cameras are designed to work. P, Av, Tv and M modes all meter for flash in different ways. See the section on “EOS flash confusion” for details. Here’s the short version, which repeats some of the points made in previous FAQ questions.
Keep in mind that the camera meters for ambient (existing) light conditions and flash illumination independently.
P (program) mode keeps the shutter speed between 1/60 sec and the maximum flash sync speed your camera can handle. It does this so that you shouldn’t need a tripod, even if light levels are low. It then tries to illuminate the foreground using flash.
Av (aperture priority) and Tv (shutter speed priority) modes set the shutter speed or aperture to expose for the existing light conditions correctly. They then fill in the foreground using flash. If light levels are low you will need a tripod to avoid blur.
M (manual exposure) mode lets you set both aperture and shutter speed to be whatever you want. The camera then automatically controls the illumination of the foreground subject using flash.
Flash metering systems used by Canon EOS.
Electronic flash has come a long way since Harold “Doc” Edgerton, an American researcher and inventor, made modern electronic flash photography a reality in 1931. But simple or complex, the basic principle of electronic flash remains the same - you charge up a capacitor (or “condenser”) with electricity and then release the stored energy in a brilliant split-second burst of light from a flash bulb - a glass tube filled with inert gases.
The light output changes instantly in response to the presence or absence of power being delivered to the tube, so the primary form of control you have over the light output is duration of the electrical pulse, which is switched off by a component called a “thyristor.” Old-fashioned manual flashes require you to calculate the distance to the subject and then set the flash duration time yourself; a cumbersome and error-prone process. Modern flash units automate this process completely through the use of computer-controlled electronics.
In regular photography you have two basic ways by which to control the amount of ambient (available) light entering the camera and exposing the film. You can adjust the shutter speed, which affects the duration of the exposure since ambient light is essentially constant in this context. And you can adjust the lens aperture - the physical diaphragm on most lenses which governs the quantity of light that enters the lens. (you can also use different lenses, add filters to the lens and so on, but we’re talking about the fundamental issues here)
However, flash photography is quite different since it involves split-second bursts of light. A key point to remember in flash photography is that the shutter speed of the camera normally does not have any bearing on flash exposure - an exception being FP mode, mentioned later. Light from a continuous source is affected by shutter speeds, but flash bursts are so brief - in the milliseconds - that a mechanical shutter mechanism has no way of limiting the amount of light from a flash unit that hits the film. Shutter speed only affects the amount of ambient light.
You therefore have four basic ways to control how much light from a flash unit exposes the film.
So that’s what flash metering is really all about, in a nutshell. You need to adjust the duration of the flash pulse so you can expose the film correctly and achieve your photographic goal. Determining what this flash duration should be is not an easy thing to do, however, and so camera makers over the years have come up with various automated systems to do it.
Flash metering has very different requirements from normal ambient light metering for the reasons outlined above. Ambient light metering is performed well in advance of the shutter opening. EOS cameras, for example, activate the internal light meter when you press the shutter release button down halfway. But the subject-illuminating flash pulse, however, occurs after you press the shutter release all the way. That means that the flash pulse appears after the mirror has flipped up (blocking the ambient light meter) and the shutter has opened.
There are thus two basic ways you can meter for flash automatically. First, you can measure the flash pulse as it is being emitted or second, you can send out a low-power test pulse (preflash) of known brightness first and base your light calculations on that data before the shutter opens.
These two flash metering methods are used by Canon’s automated flash metering systems. TTL and A-TTL flash use the former and E-TTL the latter. Flash units capable of E-TTL also support FP mode flash. Here’s an explanation of these technologies.
TTL (through the lens) flash metering.
As noted above, the earliest electronic flashes required the photographer to perform distance calculations by hand. Later, the first generation of automatic electronic flash units relied upon external sensors to determine the flash exposure setting. These sensors, mounted on the front of the flash unit, simply recorded the flash bulb’s light, reflected back from subject, and cut off the power when enough light for a satisfactory exposure was determined. The venerable Vivitar 283 still sold today works this way, in fact.
Of course, such external sensors were easily fooled. The sensor might, for example, cover more or less area than the lens currently in use. So Olympus pioneered through-the-lens flash metering in the mid 1970s with the OM2. Canon later included TTL flash metering in their T90 camera a decade later, and added the feature as standard with the EOS line of film cameras. It’s for this reason that the Canon T90 is the only non-EOS camera capable of using Canon’s TTL system.
TTL flash metering works by measuring the pulse of flash-generated light bouncing back off the subject and entering the lens. It actually measures this light reflecting off the surface of the film itself, in realtime, by using an off the film (OTF) sensor. The light from the flash bulb is quenched when the sensor determines enough light has been produced to achieve a satisfactory flash exposure to get a mid-toned subject.
For those interested, the OTF sensor is buried deep in the camera body, and is visible if you put the camera in bulb mode (ie: flip up the mirror and open the shutter) and open the camera back. It’s a small lens pointing back at a 45° angle towards where the film surface would be, and is located at the bottom of the camera in the ridged black area right in front of the shutter curtain. The rectangular or cross-shaped hole or holes immediately in front of it are the autofocus sensors.
The TTL sequence of operation is as follows:
One note - since the sensor records light reflecting off the surface of the film itself it will of course react differently to film with very different reflective properties. According to B&H;’s Henry Posner on the EOS list, all cameras with TTL flash are calibrated to work with the emulsion characteristics of typical colour print film and there may, therefore, be very subtle differences in flash metering when you use slide film. Since slide film has very narrow exposure tolerances (latitude) this might be an issue for you.
Cameras which
support TTL flash:
The T90 and all EOS models except the EF-M and digital D30, D60 and 1D.
Flash units
which support TTL flash:
All “E’ series Speedlites plus the 300TL: 160E, 200E, 220EX, 300EZ,
380EX, 420EZ, 420EX, 430EZ, 540EZ, 550EX, 480EG, MR-14EX, MT-24EX and 300TL.
Refinements to TTL flash, including Canon AIM.
TTL metering is more reliable than systems which rely on external sensors, but it can still be fooled. For example, a highly reflective subject or a subject in white surroundings can result in a lot of light reflecting back, so the resulting picture may well be underexposed as the camera quenches the flash too soon. An off-centre subject poses similar problems. Another issue is that the flash metering occurs while the shutter is open, so the camera can’t accurately factor flash in with ambient light metering.
Canon refined TTL control on their multiple focus point cameras by adding a feature they call AIM, (“Advanced Integrated Multi-point Control System”) which is basically multiple-segment flash metering. This lets the camera bias the flash exposure to the currently selected focus point, thereby increasing the chances of getting accurate flash exposure for off-centre subjects.
The AIM system means that it’s best to rely on selecting off-centre focus points for flash photography rather than using the centre point and then recomposing the image. (unless you use flash exposure lock, explained below) For more information on AIM consult the flash metering patterns section. Note that older EOS cameras with multiple-segment flash metering didn’t use the term “AIM” in their documentation - Canon came up with the marketing term sometime in the mid 90s - so the fact your multiple focus point camera doesn’t mention AIM doesn’t mean it hasn’t got it.
Nikon improved their TTL flash metering system by incorporating subject distance into flash calculations - their “3D” system. This system determines distance information by reading the current focussing distance from the lens. Canon (presumably for patent reasons, though it should be noted that many older EF mount lenses do not have the ability to return focus distance information to the camera), do not do this, and many photographers hold this as one aspect in which Nikon’s flash metering is superior to Canon’s. Though to be fair to Canon, this sort of distance measurement does not work with bounce mode or any diffusion system in which the light from the flash unit does not travel directly to the subject.
Canon’s first step in altering flash exposure design was the creation of A-TTL, or “advanced through the lens” flash metering, which was introduced with the T90 camera and continued on to the EOS series of film cameras.
A-TTL flash units (EZ series Speedlites) send out a brief burst of light during the metering phase. (ie: when the shutter release button is pressed halfway) This preflash is recorded by an external sensor on the front of the flash and used to determine a reasonable aperture to ensure adequate depth of field, particularly at short distances. The flash unit then sends out the actual scene-illuminating flash once the shutter has opened.
The A-TTL sequence of operation is as follows:
Camera units
which support A-TTL:
The T90 and all EOS models except the EF-M and digital D30, D60 and 1D.
Flash units
which support A-TTL:
Speedlites 300EZ, 300TL (T90 only), 420EZ, 430EZ, 540EZ.
Sadly A-TTL, despite its name, is of rather limited value. For one thing, use of A-TTL in bounce mode on some flash units such as the 420EZ and 430EZ results in blinding flashes of white light from the main bulb each time you press the shutter halfway, which can be very annoying to human subjects. Although these flash units use a small separate A-TTL tube to flash fairly discreet near-infrared red light during the preflash stage when the head is pointed straight on, they flash the main flash tube (white light) instead when the flash head is tilted or swivelled.
If that weren’t enough, the preflash isn’t even really used by most EOS cameras when it’s in Av, Tv or M modes, since unlike P mode you aren’t setting aperture automatically for flash metering purposes. And, unlike E-TTL, the A-TTL flash is never used for actual flash metering. The original purpose of the A-TTL preflash in those modes was to provide information to the flash out of range warning light in early EOS cameras - the 630, RT and 1. Canon had to drop that whole system for patent reasons by the late 80s, but the A-TTL preflash in non-P mode still lives on as a kind of useless appendix in most A-TTL flash units.
It’s interesting to note that the 540EZ flash avoids these problems simply by ditching A-TTL in bounce mode altogether and reverting to TTL. In fact, the 540EZ doesn’t use A-TTL for Av and Tv modes either, unlike the earlier flash units. Presumably by that point Canon decided that most 540EZ buyers weren’t going to be 630, RT and 1 owners as well.
Since the A-TTL sensor is on the front of the flash unit - behind a recessed plastic lens and not inside the camera, metering through the camera lens, it’s conceivable that a very heavy filter on the lens might result in some metering problems since the filter doesn’t cover the sensor as well. And, speaking of the flash-mounted sensors, be sure not to block it with your hand or anything for the same reason. Some flash diffusers can also present a problem in that the light spilling downwards from the diffuser can enter the A-TTL sensor inadvertently.
Finally, despite the additional complexity of the preflash circuitry, A-TTL simply ends up setting a pretty small aperture most of the time, to assure wide depth of field, which isn’t always what you want.
In short, A-TTL adequately assures reasonable flash exposure and depth of field in a point and shoot fashion in P mode. It isn’t so useful for more subtle or complex lighting techniques and isn’t useful at all in Av, Tv and M modes.
With the Canon Elan II/50 camera in 1995, Canon introduced another form of flash technology - E-TTL, for “evaluative through the lens” flash metering. E-TTL fires a low-power preflash of known brightness from the main bulb to determine correct flash exposure. It measures the reflectance of the scene with the preflash, then calculates proper flash output to achieve a midtoned subject, based on that data. It uses a preflash, but doesn’t suffer from A-TTL’s drawbacks for two reasons.
First, the E-TTL preflash occurs immediately before the shutter opens and not when the shutter release is pressed halfway. Unlike the A-TTL preflash, therefore, the E-TTL preflash is actually used to determine flash exposure and isn’t fired during the ambient (existing) metering stage. Some users may be surprised to learn that E-TTL actually fires a prefire flash before the main flash at all. Using regular settings the process happens so quickly that the preflash is difficult to notice, though you might catch glimpse of it before the mirror blackout - an exception being second-curtain sync.
Second, the preflash light is analyzed by the same evaluative metering system that the camera uses to meter ambient light. This means it meters through the lens and is harder to fool than external sensors, isn’t confused by bounced light and does not read anything off the surface of the film. For what it’s worth, unlike the TTL flash meter, the E-TTL metering sensor cannot be seen by the curious - it’s hidden away up in the pentaprism (or roof mirror in low-end EOS cameras) housing.
E-TTL is also generally superior to TTL and A-TTL when it comes to fill flash. The E-TTL algorithms are usually better at applying subtle and natural fill flash light to daylight photographs. E-TTL exposure is also linked to the current AF focus point, which in theory results in finer-grained exposure biasing than most multiple-zone TTL flash sensor systems.
The usual E-TTL sequence of operation, not counting the optional flash exposure lock (FEL) feature, is as follows:
Camera units
which support E-TTL:
All type A EOS cameras.
Flash units
which support E-TTL:
All EX series Speedlites: 220EX, 380EX, 420EX, 550EX, MR-14EX, MT-24EX.
One drawback of E-TTL is that the preflash can cause people who blink quickly to be photographed mid-blink - what EOS list member Julian Loke has referred to as the BEETTL syndrome, for “blinking eye E-TTL.” The preflash normally occurs an extremely brief period of time before the main flash, but when using second-curtain sync with slow shutter there’s enough time for rapid blinkers to react to the preflash. This apparently can also be a problem for nature photographers who photograph birds.
Another problem is that the use of preflash can trigger studio slave flash units which work by detecting the light from the triggering camera - optical slaves. This results in flash exposure going very wrong, since the optical slave is triggered too soon. The preflash can also confuse handheld flash meters, making manual flash metering very difficult.
More abstractly, E-TTL is a very automated system and isn’t well documented for the user. For instance, as noted above, Canon have never published details on the E-TTL auto fill reduction algorithm. It takes a bit of experimenting to figure out how the system is likely to respond. And there’s relatively little user selection or choice in operation modes. Most flash units don’t, for instance, let you manually choose TTL, A-TTL or E-TTL flash metering at will (though the 550EX lets you disable E-TTL).
Finally, not every E-TTL feature is supported by every type A body and E-TTL flash unit. Some wireless E-TTL features and other functions such as the modelling light, for example, require both newer type A EOS bodies like the EOS 3 or EOS 30 and flash units like the 550EX or 420EX. Part III of this article describes which features are available for which combinations of camera body and flash unit.
FP (focal plane or high speed sync) flash mode.
Synchronizing flash exposure with both curtains of focal plane shutters was as much of a problem in the days of single-use flash bulbs as it is today with electronic flash units. For that reason flash bulbs designed to work with focal plane shutters were developed. Such bulbs produced light quite rapidly and sustained their light output for the full duration of the shutter opening. They were called FP bulbs.
With E-TTL Canon introduced an implementation of an electronic FP flash mode, which is a way of circumventing the X-sync limitation in certain cases, and another flash technology pioneered by Olympus. FP flash lets you take flash photos at any shutter speed you like, and works by pulsing the flash bulb at an extremely high rate - 50 KHz - simulating constant light at the cost of total light output. FP stands for “focal plane,” by analogy to the old FP flash bulbs, though Mark Overton memorably refers to it as “fast pulse” mode in his FAQ, since that’s exactly how it works today.
This mode is useful for shooting with fill flash outdoors with wide apertures. Normally you can’t shoot outdoors and use fill flash unless you stop down the lens or use very slow film. However, changing film is a nuisance and stopping down the lens increases the depth of field. If you’re shooting a portrait, say, you probably want to blur the background and the only way to do this is to shoot with a wider aperture. But the wider aperture lets in more light, and you can’t compensate by increasing the shutter speed if you then bump up against the camera’s X-sync limit.
FP mode flash solves this problem by letting the shutter speed exceed the X-sync limit and instead reach the camera’s maximum shutter speed (usually 1/2000 or 1/4000 sec). And if you’re shooting a person fairly close up, you may not be limited by the reduced light output in FP mode unless you’re trying to use it with a very small flash, like the tiny 220EX, or slow film.
Note an important point - FP mode does not help you freeze motion; the name “high-speed sync” is a bit misleading in this regard. Normal flash photography is very good at freezing motion on film, since the flash burst is so incredibly brief. However when you use FP mode flash the flash unit pulses the light output to simulate a longer-duration burst of light. Since the flash burst is not particularly brief you can’t freeze motion as easily, even with high shutter speeds. The mode is called high-speed sync since it lets you synchronize flash exposure with high shutter speeds, not that it lets you take high-speed photographs.
Since Canon’s FP mode is tied in with E-TTL technology it’s only available when using EX-series flashes attached to A-type bodies. There are two exceptions to the “type A / FP flash” rule. First, the type B EOS 1N body can be reprogrammed by Canon at great expense to support FP mode but cannot support any other feature associated with E-TTL even when reprogrammed. And second, the digital D30 and D60 support FP mode on external flash units but have E-TTL compatible internal flashes which cannot support FP mode.
FP mode is indicated on type A cameras and flash units by a small lightning bolt symbol and the letter H, for “high speed sync.”
Camera units which support FP mode flash:
All type A EOS cameras plus the EOS 1N if reprogrammed as above.Flash units which support FP mode flash:
All EX series Speedlites: 220EX, 380EX, 420EX, 550EX, MR-14EX, MT-24EX.
TTL and E-TTL and EOS film cameras.
All film-based Canon EOS cameras at the time of writing support TTL flash metering - the one exception being the oddball Canon EF-M, which was a manual-focus camera that could accept EF-mount lenses but which lacked both autofocus and TTL flash circuitry as a cost-saving measure. (you had to buy an optional flash unit with an external sensor, the Speedlite 200M, if you wanted to do flash photography with the EF-M) All film-based EOS cameras with built-in flashes rely solely on TTL for flash exposure control of those internal flash units.
Canon cameras designed prior to the Elan II/EOS 50 of 1995 don’t support E-TTL. With the release of this camera Canon divided their camera bodies into two types - A and B. Type A bodies are bodies which support E-TTL, FEL and FP flash technologies. Type B bodies are bodies which do not.
With flash units it’s easy - if the name of the flash unit ends with the letter X (eg: 550EX, MT-24EX) then it’s an E-TTL unit. If it ends with anything else (eg: 430EZ, 480EG) then it is not.
However, there are three points of note here. First, Canon continued designing and selling type B bodies for many years after the introduction of the Elan II/EOS 50, such as the EOS 3000 and venerable EOS 5/A2, so the date you bought your camera won’t tell you if it’s a type A or B body. Second, since Canon came up with the whole A/B naming convention in 1995, older cameras are obviously not described as being “type B” in their manuals. And third, type A simply means support for E-TTL, FEL and FP mode - it doesn’t mean that the camera necessarily supports other recent flash features such as wireless flash ratios or modelling flash.
TTL and E-TTL and EOS digital cameras.
All current Canon digital cameras with hotshoes - both the D30, D60 and 1D digital EOS cameras and the non-EOS PowerShot Pro 70 IS, Pro 90 IS, G1 and G2 point and shoot digital cameras - support E-TTL only. Even Canon digital cameras with internal popup flashes are E-TTL only. (though if you want to use flash with a non-EOS camera you should probably check out Kevin Bjorke’s page for its limitations. Canon have also written a letter to D30 users concerning proper use of EX flash units)
This means that only EX flash units can be used with Canon’s current lineup of digital cameras. Older E and EZ flash units do not work correctly. You can sort of get the flash units to work in manual flash mode but no through the lens metering is possible.
This is presumably a cost-saving measure. Since digital bodies lack film they can’t use regular off the film flash sensors for TTL metering. The mirrorlike surface of a CMOS or CCD imaging chip has very different reflective properties from film, and so it takes a form of emulation for a digital camera to work with such a system correctly. And since Canon are clearly switching over to E-TTL in general, only supporting TTL on their new flash units for compatibility with older cameras, it’s not surprising that their digital products are E-TTL only.
It’s not clear how the first generation of Canon digital SLRs (developed in conjunction with Kodak), the discontinued EOS DCS1, DCS3 and D2000 cameras, support flash. It seems the DCS cameras theoretically support TTL, albeit poorly, and the D2000 supports E-TTL as well, but Canon’s Web site doesn’t really say.
Type A bodies, with support for E-TTL flash, FEL and FP mode:
EOS Elan II(E), EOS 50(E)/55
EOS 3
EOS D2000 (digital)
EOS Rebel G/500N/New EOS Kiss
EOS Rebel 2000, EOS 300/Kiss III
EOS Kiss IIIL
EOS IX, IX 7, IX Lite, IX 50 (APS)
EOS Elan 7(E), EOS 30/33/7
EOS 1V
EOS D30 (digital)
EOS D60 (digital)
EOS 1D (digital)
EOS 3000NType B bodies, with support for TTL and A-TTL only:
EOS 600 series - 600, 620, 630, 650, RT
EOS 700, 750, 800
EOS 1
EOS 1N, 1NRS
EOS 10/10S/10QD
First generation Rebel series - Rebel, Rebel S, EOS 1000 and all 1000 variants, Rebel II, Rebel X, XS/EOS 500/Kiss
EOS Elan/100
EOS A2(E), 5
EOS 3000/88, 5000/888
EOS system compatible flash units.
This document is concerned primarily with two types of flash technologies built by Canon for use with their EOS cameras - the pop-up integral flash units built into most low and midrange EOS cameras and the external shoe-mounted Speedlite flash units which can be attached to any EOS camera.
I do not discuss studio flash units (large flash units for studio photography, usually powered by AC current and not batteries, and called “studio strobes” in North America) in any detail here.
Most Canon EOS cameras contain integral flash units, built into the housing that contains the camera’s prism or mirror. Some are motorized and pop up immediately all basic (PIC or icon) modes except sports and landscape if the camera thinks you need flash, or upon the touch of a button if you’re in an advanced (creative zone) mode. Others require the user to lift up the flash manually. One camera, the 10/10s, has a motorized flash unit which both pops up and retracts mechanically, for those interested in trivia.
These internal flash units are useful for quick snapshots and the like, but aren’t usually useful for quality photography for a number of reasons. First, they’re very small and offer very low output levels - low guide numbers such as 11 or 13. Second, they’re located quite close to the lens axis and so are very likely to cause the redeye effect when photographing people. Third, since they don’t extend very far above the top of the camera body their light is easily partially blocked by large lenses or lenses with large lens hoods. And fourth, they don’t offer any tilt or swivel options and generally have coverage areas of only 28mm or 35mm at the wide end.
However, since they’re built-in they’re obviously eminently portable and handy at a moment’s notice. They’re useful for applying a touch of fill flash when outdoors. And they recharge very rapidly as they use the camera’s lithium battery as a power source. This latter can be a bit expensive, though, as using the built-in flash runs down the camera battery alarmingly quickly.
No EOS camera lets you use the internal flash when an external flash unit is mounted on the hotshoe. In fact, external flash units physically prevent the internal flash from being raised. Additionally, EOS cameras with motorized internal flashes have small electrical switches built into the hotshoe which detect the presence of a device and disallow internal flash popup. So the internal flash won’t rise automatically if anything’s in there - even, say, a hotshoe-mounted spirit level or something else non-electrical. These switches, incidentally, have been known to stick, rendering the internal flash inoperable.
None of the professional EOS cameras (1, 1v, 3, etc) have built-in flash units, for the reasons listed above and possibly also because of the difficulty of waterproofing a popup flash mechanism. All EOS film cameras use TTL only for internal flash control. At time of writing the only EOS cameras to use E-TTL for internal flash unit control are the digital D30 and D60, though their internal flash units do not support FP mode.
Cameras with internal flash units:
Please consult the flash coverage list.
Basic (PIC) modes and external flash units.
Older EOS cameras, such as the 10/10s and Elan/100, have PIC (“programmed image control” or icon) modes that don’t handle external flash units correctly. The PIC modes which use flash when necessary (all but landscape and sports) are designed to use the internal flash and are optimized for its characteristics. Check your manual to see if your camera fits in this category - probably pre 1995 or so.
Newer EOS cameras, such as the Elan II/EOS 50 or Elan 7/EOS 30, can use an external flash unit with the PIC modes. But nonetheless for best control you’re better off using one of the “creative” zone modes anyway - P, Av, Tv or M. Remember that there are significant differences in the way each of these four modes handle flash exposure.
Because the full auto (green rectangle) and PIC modes afford very little control over the way the camera works I primarily discuss how flash works with the “creative” zone modes.
Canon external flash unit types.
There are three basic types of external flash units considered here - standard hotshoe flashes, handle flashes and macro flashes. (as noted above, studio flashes of the kind that require household AC power are not discussed in this document)
For a complete list of Canon’s EOS flashes over the years check out Dave Herzstein’s comprehensive EOS flash page.
Nomenclature of external flash units.
Canon have made a number of flash units compatible with EOS cameras. The naming system is fairly logical - they’re given names such as “Speedlite 550EX”. Here’s what the parts of the name mean:
Flash units which end with “Z”, such as the 430EZ, are flash units with zooming motors and support for A-TTL but not E-TTL. The 480EG flash has a built-in grip. Flashes end in “E” only, such as the 200E, are basic models with neither zooming heads nor E-TTL support.
Although this naming system is very reasonable it does mean it’s easy to confuse different models which happen to have identical guide numbers. For example, the 420EZ and 420EX flash units are very different indeed. The former was top of the line for its time, but supports only TTL and A-TTL and is now quite dated. The latter is considered a midrange flash unit in today’s lineup, and although is technologically much more sophisticated as it supports both E-TTL and wireless flash slave mode, it lacks stroboscopic mode and has no manual controls.
Older Canon Speedlite flash units.
Older Canon Speedlite flash units which lack the letter E in their product name were not designed for EOS cameras. There were Speedlite A models (eg: 199A) for old A-series Canons such as the A1 and AE1 and Speedlite T models (eg: 277T) for T-series Canons such as the T50 (but not the T90) and various other special-purpose models.
You can put these older flashes on your EOS camera and they’ll trigger OK when you take a photo, but they can’t use modern automated flash metering. So you have to either use them in auto mode if they have such a setting (set your camera to a shutter speed up to the camera’s X-sync), dial in manual power and calculate the flash distance yourself if they have manual controls or else expect the flash to fire at full power.
I don’t know if all earlier Speedlite products have safe triggering voltages or not. The list maintained by Kevin Bjorke on his Web site suggests that T series flash units are OK and most A series and older flash units are in a grey zone, but you should probably check for yourself.
The one exception is the 300TL flash unit. It was designed for the old Canon T90 camera, and its features are not fully supported by EOS cameras. However it can be used with EOS cameras as a basic TTL flash unit even though it lacks an E designation.
Canon sell and have sold a number of different standard hotshoe flash units, which can be divided into three basic categories. Have a look here for a brief comparison of E and EZ (ie: non-EX) flash units.
Basic flash units - 160E*, 200E, 220EX.
These small devices have very limited power output - you could think of them as little flash units for those cameras which lack built-in flash. The 160E and 200E support TTL only, but the 220EX supports both TTL and E-TTL. They do not zoom, swivel or tilt, but are extremely compact and lightweight. The tiny 160E is the only Canon flash unit which does not use four AA cells - it uses a lithium 2CR5 battery instead. That means that it’s very small and light, but expensive to operate as lithium batteries are very costly.Midrange units - 300EZ*, 380EX*, 420EX.
These flash units have more power and have zooming flash heads but no manual controls. The 300EZ supports TTL and A-TTL and the EX units support TTL and E-TTL. When it comes to flash heads, the 300EZ neither tilts nor swivels, the 380EX tilts only and the 420EX both tilts and swivels. The 420EX can also serve as a slave unit in wireless E-TTL flash.The high-end units - 420EZ*, 430EZ*, 540EZ, 550EX.
These are of course the largest and most powerful flash units of the standard type. They support the most advanced Canon flash technology at the time they were introduced; TTL and A-TTL in the case of the EZ units and TTL and E-TTL in the case of the 550EX. They also have both manual controls and tilt and swivel flash heads. Of these the 420EZ is the most limited - it has no flash exposure compensation, for example.* Discontinued product at time of writing.
Canon still make one large flash unit of this type, the 480EG. It’s basically a flash bracket with a massive heavy-duty flash attached to the side. The camera sits on the bracket and is held in place via the tripod mount. This type of handle flash is sometimes jokingly referred to as a “potato masher” flash unit.
The 480EG is a high-output flash unit meant for press or wedding photographers, but hasn’t been updated in some time and is a TTL-only flash (no A-TTL or E-TTL support). Nowadays people usually just buy flash brackets and put a regular 550EX flash unit on them for this sort of application. This setup also lets you mount the flash unit vertically above the lens rather than to the side only, like the 480EG. But if you want the sheer light output you can’t beat the 480EG or similar flash units from manufacturers such as Metz.
The 480EG is also the most powerful flash unit that Canon make, even though its advertised guide number is only 48 and thus lower than flash units like the 540EZ or 550EX. This is because the 480EG’s flash head does not zoom and cannot, therefore, automatically concentrate light output when used with longer focal lengths. See the sections on guide numbers and zooming flash for a more detailed explanation.
The unit does, however, ship with a wide-angle attachment and a telephoto attachment which can be clipped on and used to diffuse or concentrate the unit’s light output. (the telephoto attachment gives the unit a guide number of 68 at 135mm, so you may occasionally see the 480EG being misleadingly described as a flash unit with a guide number of 68.) The 480EG has twin bulbs, a slave connector and full tilt and swivel capabilities, but it does not support second-curtain sync or exotic features like stroboscopic flash.
Interestingly, it also has an old-style external auto flash sensor built in. So if you have an older pre-EOS camera that doesn’t support TTL metering - or if you want to avoid TTL metering altogether for some reason - you can still use it. You can even use the optional Synchro Cord 480 to link the flash to a camera via a PC socket.
Canon sell three flash units for macro (closeup) photography. Two, the TTL-only ML-3 flash and the E-TTL MR-14EX flash, are ring-shaped flashes designed to fit directly around the end of a macro lens. The other, the luxurious and hugely expensive E-TTL MT-24EX “macro twin lite,” contains two small flash tubes on the end of a pair of short swivelling arms which can be adjusted independently and which can also be clipped to a ring that fits macro lenses. (note that the older ML-2 macro ring lite flash supports TTL, but only with the T90 camera - Canon states that it cannot meter TTL reliably with EOS cameras)
Macro flashes are specifically designed for closeup photography, and let you take shadowless photos of small objects. Since each macro flash has two independent flash tubes you can adjust the lighting ratio between them, for diffused shadows. It was trendy for a while in the 1990s to take fashion photos with large ring flashes to get a flat shadowless look to the models, but macro flashes aren’t really powerful enough to do this sort of thing well.
For some bizarre reason people consistently mistype “macro” as “marco,” as if the flash unit type were of Italian provenance. Please note that it’s not.
A number of manufacturers other than Canon build flash units that can be used with EOS cameras. Here’s a bit of information on them.
Note that one problem with third party flashes is that Canon have not published the data protocols used by its cameras, lenses and flashes. So any flash unit designed to be compatible with EOS TTL, A-TTL or E-TTL flash metering has been reverse-engineered based on the behaviour of existing products. It’s quite possible that Canon will release a future camera that uses some modification to the protocol and your flash won’t work with it.
This may or may not be a big issue for you, but it’s worth keeping in mind as it has been a problem in the past. For instance, the EOS 30/Elan 7 apparently does not work with some Metz adapters - see the note below.
Achiever, a Hong Kong third-party manufacturer of flash units, point and shoot cameras and various sundry other products like paper shredders, list a number of flash units that they say work with EOS cameras.
I understand that their products are all TTL only. But useful feature lists of their products aren’t published on their site at all, so who knows?
Metz.
Metz, a respected German maker of flash units, sell quite a few “Mecablitz” flashes that work with EOS cameras by means of an adapter system. Photozone list some of them - the 54MZ-3, 50MZ-5, 40MZ-3, 40MZ-1, 40MZ-3i, 40MZ-1i, 40MZ-2, 40AF-4 and 32MZ-3 - and describe their features. The Metz range is, in fact, much more extensive than Canon’s, and Metz offers features that Canon do not - such as flash units with memory settings, built-in secondary reflectors, clip-on coloured filters and audio warning signals.
Metz’s Web site has an excellent listing of which features are available with which Canon cameras and what adapters are required, though some of the vocabulary has been translated rather literally from German and may be unfamiliar. A “lighting control indicator” is what Canon call a “flash exposure confirmation” light, for example. An “AF measuring beam” is the confusing name for the “AF assist light” or “AF auxiliary light.”
Note that some users of Metz products have reported that the SCA3101 adapter, which works using TTL with older Canon-compatible bodies, will not work with the Elan 7/EOS 30. Even though the Elan 7/EOS 30 supports TTL on Canon flashes you must apparently use the SCA3102 Metz adapter. So you’re best off consulting the Metz site and, preferably, doing some testing of your own before buying. Note also that Metz have a wireless flash triggering system, but it’s not compatible with Canon’s.
Sigma, Japanese maker of many third-party lenses, build four flash units compatible with Canon EOS. Two are TTL - the EF-430 ST and the EF-500 ST, and two are E-TTL - the EF 430 Super and the EF-500 Super. Some of these flash units are listed on Photozone.
The EF-500 Super is particularly well regarded by a lot of EOS users, since feature-wise it’s nearly identical to Canon’s 550EX, which costs twice as much. The Sigma flash is not built as sturdily as the Canon, but it’s hard to argue with the price. It even has wireless capabilities compatible with Canon’s system and has the ability to operate as an optical slave. For more information on this flash unit, specifically how it compares with the 550EX, please consult the brief article co-authored by Jim Strutz and myself.
German photo accessory marketer Soligor sell a few Canon-compatible flash units; likely rebranded products. Their Web site lists some details. The flashes appear to be TTL only.
Sunpak, a Japanese marketer of photo products, sell the TTL-only AF4000 and AF5000 flash units. Finding useful information on the massively amateur-looking Tocad America Web site, their US distributor, is pretty hopeless, though. Good luck.
American camera accessory and snapshot camera marketer and designer (they don’t build products) Vivitar sell the 283 and 285HV flash units. These are self-contained flashes that rely entirely on their built-in flash sensors - they don’t support TTL metering of any kind. In fact, Vivitar apparently pioneered the autoflash concept with the 283, which is probably the best-selling flash unit of all time.
283s and 285s are relatively cheap and commonly used by photo professionals as remote flashes triggered by optical slaves and so on. You should be aware, however, that older models have a very high trigger voltage that can damage EOS cameras. Newer models are fine, but check first before attaching any such flash unit to your camera, just to be sure.
Vivitar also sell a number of EOS-compatible flashes, some of which are said to be rebranded Sigma products. There’s a list of their flash units on their Web site, and several are said to be Canon compatible, though TTL only. Their Web site is pretty uninformative, so you’re basically on your own there.
Finally, any electronic flash unit that mounts on a camera hotshoe and which has a trigger voltage of less than 6 volts will fit an EOS camera and will be fired when you take a photo. However, it won’t work with any form of TTL flash metering. See the section on “Older Canon Speedlite flash units” for details.
On to Part II.
- NK Guy, tela design.
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